Was it submerged after the satellite made its sweep? Did those volcanic-black pixels crumble and drown under their own weight? Have military censors deliberately obscured the truth? Australian explorers who sailed the South Pacific for 25 days in search of the landmass known as Sandy Island, after spotting it on Google Earth, have returned none-the-wiser. And it's not just Google that is apparently inaccurate -- a Coral Sea island in the same position also appears on Yahoo, Bing and even iOS maps, as well as on the Times Atlas of the World under the eerily appropriate name of Sable Island, which could be interpreted as "Very Dark Black Island."

The depth of the ocean is around 1,400 meters at these coordinates (-19.225583, 159.938759), which is precisely why the the University of Sydney's maritime researchers went looking -- it would be an extremely unusual outcrop if it actually existed. One down-to-earth explanation is that the entity is the cartographic equivalent of a watermark, allowing the mapmaker to tell if his work has been pirated, but no doubt there are other possibilities. Dr Maria Seton, fresh from a fruitless month on the waves, insists she plans to "follow up and find out."